metropolis vs San Juan

metropolis and San Juan both are nouns.

Word	Noun	Adjective	Verb	Adverb
metropolis	Yes	No	No	No
San Juan	Yes	No	No	No

metropolis (noun)	San Juan (noun)
people living in a large densely populated municipality	the capital and largest city of Puerto Rico
a large and densely populated urban area; may include several independent administrative districts